When a baseball bat or softball bat impacts a ball, energy is transferred from the ball to the bat, in the form of deformation (radial and transverse), noise, and heat. When the ball strikes a location of the bat that is in the proximity of a primary vibration node, and/or at the intersection of a primary vibration node and the center of percussion (COP) of the bat, the bat experiences little or no vibration. This is known as a “sweet spot” hit. Alternatively, when the ball strikes a location of the bat that is not in the vicinity of a primary vibration node or the COP, the bat deforms into its fundamental and harmonic mode shapes. The magnitude of this deformation is a direct function of the mode that is excited and the distance from the vibration node to the impact location. If the acceleration of the bat into this mode shape is significantly high, the bat will vibrate and produce shock waves.
Shock waves travel at a very high velocity and, depending upon their energy, can actually sting a player's hands. This event is the direct result of the feedback that a player receives when hitting the ball at a location away from the “sweet spot” of the bat. This is also known as an “off-center hit,” because the “sweet spot” of a bat barrel is typically located at approximately the center of its length. The sting resulting from off-center hits may be distracting and painful to the player, and is therefore undesirable. To minimize sting, and improve the “feel” of the bat, shock waves resulting from off-center hits must be attenuated or absorbed prior to reaching the bat's handle.